I see no reason that life can't exist on desert planets. As long as the atmosphere contains some water vapor (evident by clouds) then of course life would be possible there. They should, however, be rarer than Terras With Life, though.

I'd only want it in if you could see animals or civilization on the desert or Titanian planets. That is what makes Terra's with life awesome, you can see the greenery of the forests and grassy fields while life on a desert or titan would be harder to represent since it would probably would not be on permanently sticking it out on the surface of a desert or titan planet.

Also this is why I pass over Oceanic planets with life, they look just like the ones with no life, unless I'm missing something about them.

Even here on Earth, we have extremophiles that can thrive in environments that would never support anything else. Perhaps we could have mats of fungus or bacteria in place of vegetation for the more "out there" worlds. They could grow along the coastline, have different "moldy" textures, and perhaps have more exotic colors, like red or periwinkle.

Well, there may be sillicon-based life out there. If so, it'd likely be mainly on hot worlds, I think to help deal with some of the problems Silicon chemistry would have (the fact that SiO2, unlike CO2 is a very unreactive solid commonly known as "sand", for example).

The atmospheric life in gas giants might give the atmosphere a green hue, if it's photosynthetic. In fact, that's what I usually consider the green atmospheres to be, floating algae.

The one thing I've always been skeptical of is complex life on gas planets. I can see some durable little microorganisms floating around the gas taking what they need. I suppose that you could have larger life forms but no societies or groups as we know them- the violent winds wouldn't allow it.

If we ever encounter alien life, the last thing we could ever expect is DNA or a very similar molecule. In the entire universe, the odds should permit similar life with genetic structures similar to ours, but only because it's possible. We probably wouldn't find another planet with DNA (or similar structures) within a gigaparsec radius of ours. If genetic information is passed down, it will be done in some other form.

As for other chemestries- we should assume all alien life (aside from what I mentioned) is based on other chemicals. We are "carbon based" because of our DNA, but Life on earth contains lots of oxygen (and hydrogen- guess what molecule I'm thinking of)- it's obvious why. Life on other planets would contain large amounts of other elements: for example, carbon. Thus, we would see biochemistry totally unknown to us. Since the fundamental building blocks of life are different, we can't use words like algae, photosynthesis, or other Earthly terms. We must be specific about what's happening. For example, if a lifeform is absorbing electromagnetic radiation for energy, it's not going to be photosynthesis as we know it. Photosynthesis is a proper noun- a term describing a specific Earthly biological process. This process will be much different in life based on different types of chemicals.

The other big assumption is about water. People use the term way too much when discussing alien life. It's just as possible for life to base itself in an ocean of hydrogen peroxide as in an ocean of dihydrogen monoxide, or any other chemical which takes the form of a liquid. "Liquid" and "ocean" are acceptable for speaking generally about the subject. "Water" is acceptable only when referring to biochemistry based in H2O.

I agree with the fact that large amounts of types of life could exist.

Earth's life was created in water (this is a massively accepted hypothesis), uses carbon as a fundamental brick, nitrogen and oxigen. But most of the scientists believe that life could exist in ammonia oceans in some very cold places, or in methane (I don't talk about sulphur dioxyde, phosphine and silane). Life could use silicon instead of carbon as a tetravalent atom, phosphorus instead of nitrogen, sulphur instead of water...

Just with that, we can have 24 differents forms of life...

Morever, the elements of life could be dextrorotatory or levorotatory. For exemple, almost all the amino acids (except the glycine) found in Earth's life are levorotatory.

The common DNA is not the only way to store genetic information. We could imagine DNA with less or more than 4 nucleobases, forms of life with less or more than 20 amino acids, with a different genetic code, or a very different thing...

Gathering energy could be done by several ways (photosynthesis... ), but differents ways can exist in one planet.

I know that functional DNA with a different basis than carbon has already been synthetically produced. I can't for the moment recall what it's based on, possibly Nitrogen... Then there's xDNA which is essentially an expansion of the bases (keeping the original structure but expanding on it), although the implications aren't exactly clear to me at this time. That being said, if you're going to discuss what forms of life might exist, you might be required to discuss what life is, and that is a really tricky discussion... Not to mention the difference between sentient and not-sentient and its part in what life is.

Personally, I think this whole thing may need to be simplified to a point where there's the following: Carbon-based life (more or less like we know it, i.e. unicellular, fungi, multicell, animals. Plants... Although they're not very different from fungi, essentially) Silica-based (either similar to carbon-based or crystaline - sentience would be pretty viable through natural semi-conductor brain building ) Nitrogen-based (similar to carbon-based, but different environments? Perhaps the kind of thing one might expect at a gas giant).

I'm not sure if it would be worth the hassle to figure out what else would be possible, because then you'd have to start considering things like sentient nebulae and whatnot... Although... I must admit a type of non- or semi-sentient life form that lives exclusively in space would be fascinating... Sailing the solar and interstellar winds...

Energy sources are abundant throughout the universe, really... Even here on Earth there's life that thrives far away from the light of day, be it in caves or under the deep blue sea. And that's on a world where climate conditions are pretty optimal for this type of life and with plenty of sunlight to go around, so go figure! I think the only real limitation as to where life can exist is meeting the conditions to initiate the process; having the right chemicals in roughly the same place and a source of chaos to get the whole thing going, basically...